This invention relates to the field of transmissions, more particularly to multi-speed bicycle transmissions, and more particularly to multi-speed bicycle transmissions which are located at the pedal hub and are drive pedal actuated.
Bicycle transmissions are well known in the art, and are used to change the bicycle speed ratio, i.e., the ratio between the number of revolutions of the bicycle pedal crank and the number of revolutions of the bicycle tires in response to the pedal crank rotation. Although numerous types of transmissions have been tried or suggested, most transmissions are of three, five, ten, twelve or fifteen speed varieties. In a three-speed transmission, there are three speed ratios, in a five-speed transmission, five speed ratios, etc.
In a typical bicycle, the bicycle rider pedals a crank rotatably mounted on a crank shaft in a crank hub, and a sprocket, geared or bolted to the pedal crank shaft, rotates in response to pedalling. The sprocket is in turn linked to a drive chain which is also linked to a sprocket on the rear wheel. By pedalling the bicycle, the rider causes rotational movement of the pedal sprocket, which in turn rotates the rear wheel sprocket and rear wheel through a linked chain. Both the rear wheel and the pedal hub may contain the transmission elements required to effect different ratios of rear wheel to pedal hub rotation.
One commonly employed bicycle transmission is the derailleur-type transmission. In this configuration, the rear wheel hub, and in some cases the pedal hub, have a series of different diameter sprockets on a common axis. A bicycle chain is meshed with one of the gears on the rear wheel hub and one of the gears on the pedal hub. A chain finger moves the bicycle chain from one sprocket to another sprocket to effect gear ratio changes by changing the combination of gears in mesh through the chain. In a ten-speed bicycle, the rear wheel will typically have five driven sprockets and the pedal hub will have two drive sprockets.
The major disadvantage of the derailleur system is that the working components are exposed to abusive road conditions. If the derailleur or sprockets become bent or misaligned, the derailleur will no longer move the chain over the full row of gear sprockets. Further, mud or other debris can pack the gear train, causing limited derailleur movement and loss of full speed range capability. Also, because the derailleur is controlled by a cable, the rider must actuate levers to cause derailleur movement. Commonly, the cable may slip, or the lever, cable and derailleur may become misaligned, thereby causing the derailleur to lose full speed range actuation.
Several transmissions have been marketed or described in which the transmission components are located on the crank pedal hub U.S. Pat. No. 3,812,735 discloses a transmission which employs a shaft slidable pawl actuator to engage a selected one of a series of shaft mounted gears through gear pawls located on their inner diameters. In this patent, the pawl actuator is actuated by a lever located adjacent a sliding rotating sleeve on the shaft. The sleeve contains a circumferential slot and a pin on the lever is located within the sleeve. The lever is hinged to permit the pin to be moved along the longitudinal axis of the shaft, thereby moving the sleeve and attached pawl along the shaft. The actuator arm is thus locatable beneath one of the gears to cause a pawl to engage the gear.
U.S. Pat. Nos. 4,419,905; 4,283,969; and 4,305,312 to Lapeyre, disclose a pedal crank mounted transmission in which reverse pedal rotation actuates transmission speed ratio shifts. These patents disclose a multi-speed pedal hub-mounted transmission in which the output range is selected by the axial actuation of a pawl actuator along the inner diameter of a series of different diameter range gears mounted on the pedal shaft. The pawl actuator actuates a locking dog, or pawl, at the inner circumference of the gear to selectively engage the gear into locked rotation with the shaft. The pawl actuator is located in a slot in the pedal shaft, and is actuated by a sleeve located on the pedal shaft.
To effect pawl actuator movement, the sleeve includes a pair of diagonal opposed splines projecting therefrom with one side tapered and the other normal with respect to the circumferential surface of the sleeve. A spring-loaded shift control member with a pair of spaced cylindrical projections thereon is disposed about the circumference of the sleeve. The projections are axially spaced approximately equal the axial component of the diagonal sleeve splines and disposed to ride on the circumferential surface of the sleeve. When the bicycle pedal is cranked in a forward direction, the cylindrical projections slide over the tapered portion of the splines. However, if pedal motion is reversed, the normal surface of the sleeve spline engages the projection, and the axial component of the sleeve spline and the attached sleeve slide along the shaft. The pawl actuator is permanently attached to the sleeve, and the axial movement thereof causes an arm on the pawl actuator to disengage from a pawl adjacent the inner diameter of one drive ratio gear and engage a pawl adjacent the second drive ratio gear. Likewise, further shifts to higher gears, or shifts to lower gears, may be accomplished by movement of the pawl actuator arm.
The drive ratio gears are located on the pedal shaft and are meshed with an equal number of complementary spur speed change gears. Each drive ratio gear is meshed with one spur gear. The three spur gears are splined together, so that rotation of one causes rotation of all three. The drive ratio gears are free to rotate about the pedal shaft unless engaged by a locking dog or pawl. The first drive ratio gear is directly coupled to an output sprocket, which is meshed to a rear wheel sprocket or sprockets by a drive chain.
To cause gear shifts, the bicyclist simply reverses pedal rotation to cause the sleeve and attached pawl actuator to move axially on the pedal shaft, thereby causing one locking dog, or pawl, to disengage the initially engaged gear and a second locking dog, or pawl, to engage the subsequent gear. This causes the output gear ratio to change via the change in drive gears, through the spur gears, and back through first drive gear, which is keyed to the output sprocket. Although the Lapeyre device as disclosed in these patents teaches a reverse pedal rotation actuated transmission, the disclosed device is difficult to assemble and maintain.
U.S. Pat. No. 4,376,394 to Lapeyre, discloses another type of shifting system for use with the pawled drive and idler gear arrangement. In this system, the sleeve contains two concentric rings which form a groove in the sleeve about its outer circumference. A cable actuated lever is disposed in the seat post frame tube in alignment into the pedal crank hub, and the lever slides the sleeve and accompanying pawl actuator along the pedal crank shaft to cause gear shifts. The major disadvantage of this device is that it uses a cable which is connected to a shift lever located on the bicycle. The rider must commonly look away from the road to shift the transmission, and the cable may become disengaged or loose, causing erratic shifting. Further, the location of the cable-actuated lever about the pedal crank is critical, and even minor deviations in location can cause shifting to be erratic or impossible. Finally, if the bicycle owner decides to remove the transmission, a hole remains in the housing which will permit the entry of foreign material.
It is also known to employ reverse pedal rotation using a plastic sleeve mounted on the pedal shaft for axial sliding thereon. The sleeve contains opposed diagonal slots therein, and each slot has a wall which is normal to the axis of rotation and a second wall which is sloped. A pawl actuator is disposed in the sleeve for axial engagement of pawls on the inner diameter of the range drive gears. A spring-loaded pin is disposed through the wall of the pedal crank housing. As the pedal is cranked in the forward direction, the pin enters the diagonal groove at one end and slides over the sloped wall. As the pedal is turned in a counterclockwise direction, the pin engages the normal wall of the groove, which causes the sleeve to slide axially on the shaft. This movement causes the pawl to disengage one range drive gear and engage a different range drive gear. The diagonal slots on the opposed side of the sleeve, i.e., disposed thereon by 180.degree., move the sleeve in an axially-opposed direction.
The major disadvantage of this design is that the pin must be mounted on the exterior of the pedal housing to a close tolerance to guarantee alignment of the pin with the pedal shaft and slots. This is commonly a difficult problem, because different thicknesses of bearing cup flanges located in the crank hub will cause the pedal shaft and slots to align differently with the pin, which could render the shifting mechanism inoperable. This prevents the application of this transmission by a bicycle owner to an existing bicycle, because an expensive jig or pattern must be employed to ensure proper placement of the pin. Also, the pin is subject to environmental wear and tear, lending itself to being bent or broken which will prevent shifting of the bicycle. Further, once the pin hole is drilled, it is undesirable to revert back to the original pedal crank housing configuration because the hole will let grease out and dirt in.